Tunnel kiln



3 Sheets-Sheet l mmm:

A. MCD. DUCKHAM I TUNNEL KILN Filed April 8, 1927 May' 13, 1930. i

May 13, 1930.

A. MCD. DUCKHAM TUNNEL KILN 5 Sheets-Sheet 2 Filed April a, 1927 K ulZElICIlruZlllIE-M a @mw .........|Hu u r.

All

Mny 13, 1930. A. MCD. DUCKHAM TUNNEL KILN Filed April 8. 1927 T5 Sheets-Sheet 3 Patented May 13, 1930 UNITED STATES ARTHUR MGDOUGALL DUCKHAM, 0F LONDON, ENGLAND, ASSIGNOR TO WOODALL- DUCKHAM (192D) LIMTED, OF LONDON, ENGLAND, A BRITISH COMPANY TUNNEL KILN Application led April 8, 1927, Serial No. 182,148, and in Great Britain December 3, 1926.

This invention relates to recuperative annular muftle kilns of the kind in Which the goods are moved through the kiln on a circular track and pass successively through a preheating zone, a zone of open firing, that isa zone in Which the goods are in direct Contact With the hot products of combustion) and a cooling zone, and wherein products of combustion admitted into the kiln chamber in the zone of open firing are Withdrawn from this zone into flues arranged in the Walls of the preheating section of the kiln.

lt is usually advantageous to remove the water vapour given up by the incoming goods in the drying section of the kiln to avoid the staining effect of this vapour in the presence of flue gases, and probably in the presence of air, upon delicate surfaces. By the present invention `Water vapour is removed under control at one or more points between t-he charging point and the zone of open heating.

ln knoWn kilns of the aforesaid kind, the pull of the chimney stack, or fan, acts only on the zone of open firing, the intention being that the atmosphere in the cooling and prelieating zones should be substantially quiescent. It has been found, however, that convection currents are set up in the atmosphere of the cooler parts of the kiln in such a Way that the atmosphere in the preheating and cooling zones is moving along more or less circular paths in the direction away from the cooler parts of the zones towards the fire zone, these convection currents not only dissipate heat from the hottest portion'of the kiln but also tend unduly to heat the goods. entering and to interfere With the proper cooling of the goods leaving the kiln. The intensity of such currents is enhanced by the presence of any air which may have filtered into the kiln. It is an object of the invention to minimize these convection currents, and according to this invention, -gases are withdrawn under control from the kiln on each side of the zone of open firing. Thus there may be provided ducts connecting the cooler parts of the kiln on each side' of the zone of open tiring With the main Waste gas flue. By these means the flow of convection currents will be arrested and further cooling air can be drawn in Without upsetting the conditions in the zone of open heating, and Water vapour can be extracted from the incoming goods before they arrive at the zone of open firing. These ducts may be controlled by suitable dampers, or the like.

ln order further to minimize the setting up of convection eddies, which Would prevent the regular heating of the goods in the zones of varying heat intensity, the moving platform may carry transverse vertical Walls substantially of cross sectional area equal to that of the kiln and spaced at intervals suited to the steps at which it is desired to operate the kiln.

To ensure complete combustion of the fuel gases before they come into contact with the goods, the combustion products, when leaving the combustion chamber, may be caused to impinge upon the sides of the moving tray or platform.

In order to supply radiant heat from the bottom to the goods on the tray, the sides of the moving tray may have a series of radial flues, opening into an annular central flue or T channel, extending throughout the entire length of the kiln. In this manner the goods may be exposed to radiant heat from below as Well as from the sides and top.

In order to ensure a heating of the goods as even as possible in the lzone of open liring.y the inlets for the combustion products to the zone of open firing may be arranged at the bottom of the side Walls land, with the same object in view, the outlets from the zone of open firing to the iues in the side .valls mayY also be similarly arranged at the bottom. In order to have complete control of the temperature in the muiie and of the volume of gases entering` the zone of open firing, the ports leading to and from the open zone may have regulating means.

The accompanying drawings illustrate a kiln constructed according to the invention, and also on the general lines described in Fig. 1 being a diagrammatic horizontal section through the kiln, Fig. 2 a developed vertical section, Fig. 3 a developed horizontal section and Figs. 4, 5, 6 and 7 and 8 vertical tra Cia sections on lines lef-A., B-B, C-C, D-D

and E-E respectively of Figs. l and 2.

The heating gases from the producer a pass through a. dust-catcher Z) (Fig. 6) and pipe c into the space beneath an arch (Z, meeting, as they issue into this space, air which has entered through inlets e (Fig. 4l), at the unloading Zone of the furnace and has passed throughiiues c in the side walls and flue c2 above'the. arch (l, and has thus become preheated.

The products of combustion pass down vertical fiues f from which one part of them enters'lues /Lf presentlyto be described, and the other part passes through the clearance between the travelling platform 7L and the sides of the kiln chamber into the Zone of open ring g. l This passageY of the gases against the sides of the platform is an aid to the complete combustion of the producer gas Vbefore it enters the zone g. From this zone the gases, having passed over the transverse Wall c' (Fig. 7), which travels with the platform, escape through the ports 7c at the bottom of the kiln chamber into iiues 7c in the walls of the kiln where they travel to the chimney Hue Z.

From what has been described it will be seen that the goods starting from the loading and unloadingl zone m are dried and preheated they travel through the preheating zone n, burnt as they pass through the Zone of opening firing g and cooled as they pass through the cooling zone 0 on their way back to the loading and unloading Zone m. This cycle is already known.

According to the invention the chimney flue Z maybe put vinto communication with the kiln chamber at suitable points. In the drawing two such communications are shown through l'lues p and g respectively; these fines are controlled by valves p, g and open into' lues 11 in the Walls ofthe kiln, which iues have ports r leading to the kiln chamber. The object of these communications with the chimney flue has been described above and it may be remarked that, although only two ducts p and g are shown, there may be as many as may be necessary.

For the even heating of the goods the platform is constructed with flues z/ which are radial to the centre ofrotation of the kiln and spring on each side from an annular flue s. Asthe platform' passes the heating flues f and the ports 7c hot gases aredrawn into the flues L and through Vthe annular flue-s; in this manner the platform is heated, which contributes to an even heating of the goods.

During the loading and unloading operation it is advisable .that the annular flue s should be closed. For this purpose a suitableV slide maybe inserted into the radial flue h which happens tobe immediately outside-the transverse V-rwallz' Which happens to V-ber closing the end of the tunnel; such a slide may be inserted at each end of the charging and discharging zone.

Another method of closing Hue s consists in providing slots in the platform down which slides may be pushed in order to form a diaphragm across the flue; in this case the walls z' must be so placed in relation to the slots that there is one of the latter close to each Wall closing the tunnel at the loading section.

Yet another method consists in covering the mouths of all the ilues 7L which are in the loading Zone at the time of loading.

In known kilns of this type the transverse walls subdividing the kiln chamber have been 4liked structures so that the capacity of the sub-chambers could not be varied. According` to this invention the transverse walls are temporary structures, built on the platform, it may be after the goods have been stacked thereon. To avoid the diiiiculty of having to constructfthese walls of di1nensions precisely suitable for filling the entrance or exit to the kiln chamber at the loading and unloading Zone (for the purpose of preventing entry of air at these places), there is provided at each of these points a movable and adjustable amb or lintel, as indicated at t in Figs. 1, 2 and 4. This jamb consists in a plate which slides in a vertical slot in the roof of the kiln chamber. Before each step-by-step movement of the platform, this iambfis raised and is lowered again to rest on the top surface of that transverse wall z' which happens to be in the entry to the kiln. `The jamb may be temporarilyluted to the top surface of the wall in order to ensure a tight joint.

Having thus described the nature of the said invention and the best means l know of carrying the saine into practical effect, I claim l. A rccuperative annular inutile kiln of the kind herein referred to, wherein water vapour is remoif'ed, under control, from the kiln chamber at one or more points between the charging' point and the Zone of open heating, for the purpose set forth.

2. A recuperative annular' inutile kiln of the kind herein referred to, wherein a duct connects the interior of the kiln chamber at a point between the charging point and the Zone of open heating, with the main waste gas flue. Y

3. A recuperative annular muiiie kiln of the kind herein referred to, wherein a duct connects the interior of the kiln chamber at a point between the zone of open heating and the discharging point, with the main waste gas flue.

4. A recuperative Inutile kiln of the kind herein referred to, wherein the heating gases are admitted into the Zone of open heating through ports at the bottom of the side walls of the kiln chamber and the outlets from this Zone are also arranged at the bottom of the side walls.

5. A recuperative annular muftle kiln of the kind herein referred to, wherein the transverse walls subdividing the kiln chamber are temporary structures, the position of which can be varied readily for the purpose of varying the Capacity of the sub-chambers of the kiln.

5. Arecuperative inutile kiln, comprising a waste liuc, a portion in which the goods to be lired are preheated as they pass therethrough, a second port-ion in which the goods are subjected to direct action of combustion gases as they pass therethrough, the latter portion having in one of its walls combustion inlet and outlet ports, and a third por.- tion in which the goods are cooled as they pass therethrough, said first portion of the kiln having ducts extending longitudinally of one of its walls and connecting the outlet ports of the second-named portion with the waste gas Hue, said kiln also having outlets for the withdrawal of gases between said second portion and said lirst and third portions, respectively.

7. A recuperative muflie kiln, comprising a waste gas flue and portions forming, respectively, a preheating zone, a zone of open firing and a cooling zone for goods to be fired, the portion of said kiln which forms the Zone of open firing having inlets for the admission of combustion gases to act directly upon the goods as they pass through said zone and outlets for the escape of such gases, chiots extending longitudinally of a wall of that portion of the kiln which forms the preheating Zone and connecting said outlets to the waste gas flue for heating saidl preheating Zone, said kiln having between said first and second named portions and between said second and third named portions outlets connected to said waste gas flue.

8. A recuperative mutlie kiln comprising an annular kiln chamber having a preheating zone, a cooling zone, and a zone of open firing intermediately of the preheating and cooling zones and communicating therewith, means for introducing heating gases into the kiln chamber in the firing Zone thereof, flues arranged in the walls of the preheating Zone of the kiln chamber, means for withdrawing the heating gases from the firing Zone into the said flues, flues arranged in the walls of the cooling zone of the kiln chamber and adapted to be supplied with cooling air, and controlled means for withdrawing gases from the kiln chamber on both sides of the Zone of open firing.

9. A recuperative Inutile kiln comprising an annular kiln chamber having a preheating zone, a cooling Zone, and a Zone of open firing int-ermediately of the preheating and cooling zones and communicating therewith, means for introducing heating gases into the kiln chamber in the firing zone thereof, flues arranged in the walls of the preheating zone of the kiln chamber, means for withdrawing the heating gases from the firing Zone into said flues, liues arranged in the walls of the cooling Zone of the kiln Ichamber and adapted to be supplied with cooling air, and valvecontrolled ducts connecting the interior of the kiln chamber on each side of the zone of open firing with the main waste-gas flue.

10. A recuperative muiie film comprising an annular kiln chamber having a preheating zone, a cooling Zone, and a Zone of open firing intermediately of the preheating and cooling Zones and communicating therewith, an annular platform movable in the chamber, an annular flue in said platform and radial flues branching therefrom and adapted to receive hot gases from the zone of open firing, said annular and radial lines being beneath the carrying surface of the platform, means for introducing heating gases into the kiln chamber in the firing zone thereof, flues arranged in the walls of the preheating Zone of the kiln chamber, means for withdrawing the heating gases from the firing zone into said flues, flues arranged in the walls of the cooling zone of the kiln chamber and adapted to be supplied with cooling air, and valve-controlled ducts 'connecting the interior of the kiln chamber on each side of the zone of open :tiring with the main waste-gas flue.

l1. A recuperative annular muliie kiln comprising an annular kiln chamber having a preheating Zone, a cooling zone, andV a zone of open firing intermediately of the preheating and cooling Zones and communicating therewith, an annular platform movable in the chamber, an annular flue in said platform and radial llues branching therefrom, said annular flue and radial flues being beneath the carrying surface of the platform, ports in the lower part of the side walls of the chamber in the firing zone thereof, and substantially level with the sides of the platform, means for introducing heating gases into the kiln chamber through said ports so that they impinge against the sides of the platform, liues arranged in the walls of the preheating zone of the kiln chamber, means for withdrawing the heating gases from the firing Zone into said flue, flues arranged in the walls of the cooling zone of the kiln chamber and adapted to be supplied with cooling air, and valve-controlled ducts connecting the interior of the kiln chamber on each side of the Zone of open firing with the main waste-gas flue.

In testimony whereof I have signed my name to this specification.

ARTHUR MCDOUGALL DUCKHAM. 

